This invention relates in general to heating systems and in particular to thermostatic controls for steam heating systems.
In conventional two-pipe, vapor heating systems for residential housing and large buildings such as schools, hotels and offices, steam generated in a boiler flows through mains, branches and risers to a number of radiators distributed throughout the building. Each radiator has a thermostatic steam trap connected between its return outlet and a return main for condensed water. A central thermostat or thermostats usually control the release of steam from the boiler. The steam fills the radiator until it reaches the trap where it heats a thin walled metal chamber or bellows secured within the trap. Expansion of the bellows closes a valve within the trap and thereby holds the steam in the radiator to heat the surrounding air and prevents the steam from entering the return lines. As the thermal energy of the steam is radiated into the room, it condenses into water which eventually cools the bellows, opens the trap valve and allows the condensed water to flow into the return main.
While the central thermostat and the conventional thermostatic steam trap thus provide a certain degree of control over the operation of the radiator, they do not provide control for each radiator that is independent of the other radiators. This situation leads to a substantial wastage of heat. Rooms not in use or not frequently in use may be heated the same as rooms in use. Differences in room size, local heat loss due for example to poorer insulation or an open window can also result in uneven, wasteful heating. Also during mild weather, the typically "sluggish" response of the steam radiator to fluctuations in the ambient temperature cause overheating. These problems of heat regulation and the fuel waste are particularly acute in large buildings.
A well-known arrangement for providing individual controls is a manual input supply valve at the radiator. Such valves however require at least periodic attention and are often difficult to adjust accurately for a desired heat output. As a result, they often function simply as on-off devices. Self controlled supply valves are available which to a large extent overcome these problems, but they are relatively expensive, particularly since installation requires changes in the piping. Other known techniques such as individual room thermostats, compressed air thermostats on individual radiators, and motorized valves on the risers controlled by one or more "central" thermostats have obvious cost disadvantages particularly in terms of installation, whether initial or modification of an existing steam heat system. For the motorized valves, a steam fitter must make changes in the piping to install the valves. Conventional thermostats require the services of an electrician. Moreover, these regulators tend to be slow in responding to temperature variations and/or are costly to maintain and adjust.
Another approach to regulation of a heating system has been to influence the thermostat. For example, U.S. Pat. No. 3,386,496 to O'Connor describes two heaters placed near the thermostat. The result is that the ambient room temperature can be held at, above or below a set temperature depending on whether one, none or both of the heaters, respectively, are in operation. U.S. Pat. No. 1,583,496 to Shafer describes another well-known approach, control of the thermostat with a clock to vary the heat output with the time of day. In both the O'Connor and Shafer systems, however, there is no direct, independent regulation of the radiators unless each radiator has an associated thermostat and radiator control as well as the heater or clock device.
It is a principal object of the present invention to provide an automatic thermal control system for an individual steam trap radiator, that has a low cost, can be easily installed with a minimum of skill and requires no changes in piping or rewiring.
Yet another object of this invention is to provide individual thermostatic control for a steam trap radiator that is automatically responsive to the ambient room temperature.
A still further object of this invention is to provide a low cost device for matching the heat output of a steam heat system to the varying heating requirements of different regions of a building and thereby achieve substantial fuel savings.